just render the scene to a bmap 1/4 of the screenresolution. This could look like this for example:

VIEW* s_view_blurRender = {bmap = "#256x192x32";}

If you want to use this blurred image with other shaders (for example a Depth of Field shader), don't forget to rescale it to its original size. You can do that in the shader. This could look like this:

float4 rescaledBlur = tex2D(blurMap,texcoord/4);

[edit] heh, just noticed, i downsample by 1/16, not 1/4. sorry, my fault ^^